386 PROTEIN-COMPOUNDS. 



mode of formation. Although we are unable distinctly to recog- 

 nise the presence of casein in the blood, there is no doubt that it 

 is formed there, and that it is merely separated by the mammary 

 glands. We must clearly understand the differences in the consti- 

 tution of albumen and casein before we can venture to offer a con- 

 jecture regarding the conversion of one into the other. 



Uses. The occurrence of casein in the milk, the best of all 

 kinds of food, leaves no doubt regarding the uses of this substance : 

 especially since we see how nature provides that more casein is 

 always supplied for the building up of the bodies of very young 

 animals, than is required for their future support. Casein not 

 only yields to the infant body the material by which soft parts are 

 nourished and caused to grow, but likewise conveys into the system 

 a sufficient quantity of bone-earth and lime to cause the skeleton of 

 the infant body gradually to attain its necessary solidity. 



We now proceed to notice the chemical relations of certain 

 substances which, perhaps, strictly speaking, do not belong to 

 animal chemistry, since they occur only in the vegetable world : 

 but there are two reasons, a chemical and physiological reason, 

 why they should be noticed in the present place. In a chemical 

 point of view they deserve notice, because we thus become 

 acquainted with new protein-compounds, very similar to those 

 already described, but yet differing from them, and thus obtain a 

 more perfect insight into the whole group of this class of bodies ; 

 and in a physiological point of view they are of at least equal 

 importance, for it is from them that the animal protein-compounds, 

 which we have already described, are formed in the organisms of 

 herbivorous animals, and that the solid substrata of the body are 

 deposited in the various tissues. The actual physiological im- 

 portance of these substances will be noticed when we enter upon 

 the subject of " Nutrition. 5 ' 



GLUTEN. 



Properties. This substance, to which the name pJiytocolla has 

 also been applied, is, when dried, transparent, very hard and diffi- 



